1. Field of the Invention
The present invention relates to a developing apparatus and an image forming apparatus provided therewith.
2. Description of the Related Art
An image forming apparatus that uses electrophotography such as a photocopier and a printer is provided with a developing apparatus that stores toner therein. When a developing roller in this developing apparatus has moved to a position opposing a photoreceptor drum, an electrostatic latent image is developed on the photoreceptor drum, and a toner image is formed on the photoreceptor drum.
In such a developing apparatus, the toner electrification performance is likely to decrease due to degradation of the toner and environmental changes. Consequently the toner is likely to be scattered from the developing roller. If the scattered toner scattered from the developing roller is attached on the photoreceptor drum, then it is transferred together with the toner image, and a reduction of the image quality becomes more likely as a result.
As a method for recovering scattered toner, for example Japanese Unexamined Patent Application, First Publication No. H02-210472 (hereunder, referred to as Patent Document 1) discloses a developing apparatus provided with a recovering device that is arranged so as to oppose a sleeve (developing roller). According to the technique disclosed in Patent Document 1, a conductive roller is used as a recovering device, and by applying a bias voltage to this conductive roller, scattered toner is recovered.
In Japanese Unexamined Patent Application, First Publication No. H07-319279 (hereunder, referred to as Patent Document 2), there is disclosed a developing apparatus provided with; a toner recovering roller in close proximity to a developing roller, a frictional electrification device that comes in contact with the surface of this toner recovering roller, and a toner detaching device that removes toner that has been attached onto the roller surface of the toner recovering roller. According to Patent Document 2, by contact-charging the toner recovering roller and the toner detaching device, scattered toner recovery efficiency is increased.
Accordingly, in the developing apparatuses according to Patent Documents 1 and 2, a metallic roller is used as a roller (recovering roller) for recovering scattered toner, and a bias voltage is applied thereto to thereby make the recovering roller more likely to attract scattered toner and improve scattered toner recovery efficiency.
However, in the method of recovering scattered toner with a bias voltage applied to a metallic recovering roller, as with the developing apparatuses according to Patent Documents 1 and 2, the van der Waals' force that acts between the recovering roller and the scattered toner is significant, and therefore the force of attracting scattered toner to the recovering roller is significant.
Consequently, once scattered toner has been attracted to and attached onto the recovering roller, it is difficult to remove the scattered toner even with a cleaning member attached to the recovering roller. When the image forming apparatus has been operated for a long period of time, the entire surface of the recovering roller becomes coated with scattered toner, and the van der Waals' force that acts between the recovering roller and the scattered toner is likely to be reduced. As a result, the recovering roller becomes unlikely to attract scattered toner, and the performance of scattered toner recovery of the recovering roller is likely to be reduced.
The present invention takes the above circumstances into consideration, with an object of providing a developing apparatus capable of recovering scattered toner for a long period of time without reducing recovering performance, and an image forming apparatus provided therewith.